Doctoral Dissertation Research: Sunlight stimulates a spectrum of microbial CO2 production from permafrost carbon

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We need to better understand and reduce greenhouse-gas emissions to meet the Paris Agreement goal of limiting global warming to a 1.5 ºC increase. The thawing of organic carbon stored in Arctic permafrost soils ultimately creates carbon dioxide (a greenhouse gas). Further, this process is predicted to amplify with additional global warming, however, to an unknown extent. Therefore, we need to quantify the extent to which carbon dioxide released from thawing permafrost will amplify global warming; this is one of the most urgent questions that Arctic scientists must answer. To address this, this project will make measurements to quantify how much carbon dioxide is produced when organic carbon from thawing permafrost soils flows into sunlit arctic surface waters. The project will also leverage an existing University of Michigan program called Earth Camp to engage high school students about environmental sciences through hands-on experiences and outdoor activities.As water moves through thawed soil it dissolves organic carbon. This dissolved organic carbon (DOC) then flows into streams, ponds, and lakes. Once in surface waters, both microbes and sunlight oxidize DOC to CO2. DOC exposed to sunlight is easier for microbes to oxidize to CO2 compared to the same DOC kept in the dark. However, the sunlight reaching surface waters spans a spectrum of wavelengths, from the high-energy ultraviolet (UV) to the lower-energy visible light. A critical unknown is which wavelengths of sunlight from the UV to the visible are most efficient at helping microbes to oxidize DOC to CO2. If visible light helps microbes oxidize more DOC to CO2 than currently assumed, the CO2 produced from this process could be double the current estimate because there is more visible light reaching surface waters than UV light. In addition, different wavelengths of sunlight may help microbes oxidize a fraction of DOC that, in the absence of sunlight, microbes would not be able to oxidize to CO2. This fraction of DOC that is difficult to oxidize may be some of the oldest carbon that has been frozen for thousands of years in permafrost soils. This project will test how efficiently sunlight helps microbes oxidize ancient permafrost DOC by measuring the amount and radiocarbon age of the CO2 produced from microbial oxidation of permafrost DOC exposed to UV and visible sunlight. Results from this project will enable predictions of the CO2 produced from ancient permafrost organic carbon thawed and exported to sunlit surface waters, which is critical knowledge needed to quantify arctic amplification of global warming.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.